How to make pixelated censor effect?
Compositing can be used to create a pixelated effect. Masks can be used to control where the pixelation occurs. The animation below shows an animated pixelated window.





Steps to create a pixelated effect in an animation in Blender 2.76 w/ Cycles.


Create the scene and lighting.
Add an object which will act as a mask for the pixelation region. Put this object on its own layer. See How to output ID masks as seperate files for compositing?
Setup render layers so the scene and the mask are generated as different layers.





Use nodes for compositing in the nodes panel.
Use the pixelation node to generate a version of the scene which is pixelated. Place an inpaint node before the pixelation node to ensure the pixelation works everywhere in the image. Use the mix node to combine the pixelated and original image where the mask is used to determine where it is pixelated. See the nodes setup below for an example.






The blend file for the animation is located here: